The present invention relates to Ethernet networks, and in particular, to a method for reducing errors on dedicated multi-speed Ethernet link segments.
Ethernet local area networks are in wide use today. The term Ethernet is often used to refer to all carrier sense multiple access/collision detection (CSMA/CD) LANs that generally conform to Ethernet specifications, including IEEE (Institute of Electrical and Electronic Engineers) 802.3. IEEE 802.3, for example in the version published on Jul. 29, 1996, sets forth standards for Ethernet-type networks. Ethernet also forms the technological basis for ISO-IEC (International Organization for Standardization-International Engineering Consortium) 8802-3, as published in 1996.
Basic Ethernet, such as 10 Base-T, is capable of a data transmission rate of 10 Mbps (Megabits per second). The need for greater data rates has led to the development of xe2x80x9cfast Ethernetxe2x80x9d, such as 100 Base-TX. 100 Base-TX fast Ethernet runs well, i.e., with acceptable error rates, on EIA-TIA (Electronic Industries Alliance-Telecommunications Industry Association) 568 Category 5 unshielded twisted-pair cable, sometimes called UTP-5, or CAT 5. 100 Base-TX operates with lower signal levels, and therefore requires higher quality cable and is more sensitive to electromagnetic interference than 10 Base-T. While 100 Base-TX is capable of running on Category 3 unshielded twisted-pair cable, or CAT 3, the result is often a poor link segment with many errors.
Autonegotiation is a mechanism specified in IEEE 802.3 whereby the network entities at either end of a link segment automatically determine the data rate at which the link segment will operate. Using autonegotiation, each network entity compares what Ethernet implementation it supports to what implementation network entity at the other end supports. The network entities choose which implementation to use for that network link segment according to a predetermined priority ranking. For example, 100 Base-TX full duplex has a higher priority than 10 Base-T. Most current Ethernet network entities support autonegotiation.
As an Ethernet network is upgraded from 10 Mbps to 100 Mbps equipment, link segment cabling must be upgraded from CAT 3 to CAT 5 to properly support 100 Base-TX. Because such a cabling upgrade is costly, among other reasons, networks are often upgraded in a phased or piecemeal fashion. Thus, some network cable plants may include a mixture of CAT 5 cable and CAT 3 cable. There is a good chance that a 100 Base-TX link may be inadvertently established over a CAT 3 cable. The result of attempting to run 100 Base-TX over CAT 3 cable may be high error rates and an unstable network. An unacceptably high error rate may occur even when running a 100 Base-TX over a CAT 5 cable when the cable is subject to electromagnetic interference. Such electromagnetic interference may be caused by, for example, running the cable in a cable tray alongside power cables. Once a link segment is operating at 100 Base-TX, it may continue to do so even at unacceptably high error rates.
The present invention provides a method for controlling a data rate on a dedicated multi-speed link segment in an Ethernet network between two network entities, the link segment operating at a first data rate. The method comprises evaluating an error rate on the link segment, and, when the error rate on the link segment exceeds a threshold, automatically reconfiguring the link segment to operate at a second, lower data rate.